Dizziness and lightheadedness on the second day after taking Mirtazapine could be an adverse reaction to taking too much of the drug. Mirtazapine is an antidepressant medication that also acts as a sleep aid. Mirtazapine, if taken too much, can cause adverse reactions such as drowsiness, sedation, dry mouth, weight gain, increased appetite, dizziness and fatigue. For the elderly, the dose of Mirtazapine should not exceed 45 mg, while it is also prohibited for those who are allergic to Mirtazapine. When taking the drug, it must be taken under the guidance of a doctor, do not increase the dosage without authorization, so as to avoid adverse reactions. If symptoms such as dizziness and drowsiness occur, the drug must be adjusted under the guidance of a specialized doctor, to avoid reducing the dosage privately, which will lead to a relapse of the condition.